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Powder coating vs. stone coating

Metal roofing, which is quickly gaining popularity in the U.S., is now offered in many different materials, styles, colors, and finishes. With metal roofing products now manufactured to mimic the appearance of traditional styles such as wood shake, clay tile, and asphalt shingles, customers have more options than ever before. However, when deciding what metal roof offers the best long term solution for durability and appearance, building owners need to consider the quality of the finish on the metal panels. The two main surface finishes in the industry today are powder coating and stone coating. However, they are distinctly different, with powder coating being, by far, the superior product in long-term protection and resistance to color fading. 

THE DIFFERENCE BETWEEN POWDER AND STONE COATING

While both finishes are designed to provide a protective surfacing for the underlying metal, they are quite different in composition and application. The metal base for both surfacing’s are typically made of galvanized steel or aluminum.

Powder Coating – The powder coating process involves electrostatically applying a specialized powder to the metal surface, which is cured under heat, forming a hard, protective layer. Powder coating is highly resistant to chips, cracks, peeling, chemical exposure, and typically has a smooth and even finish. The electrostatically charged powder adheres evenly to the metal surface, reducing the risks of run, drips, or uneven coating. MMR applies our patented powder coating to premium steel, with a Kynar protected paint finish already installed, for maximum panel protection.

Stone Coating – In the stone coating process, a layer of adhesive is applied to an unpainted metal surface, followed by ceramic-coated stone chips. These chips are typically made from natural minerals, such as basalt or granite, and are available in various colors to produce different looks. The stone coating acts as a barrier against UV rays, helps prevent fading, and protects the underlying metal. However, since the stone chips contain the color for the panel, once lost, color fading is evident.

WHY POWDER COATING PROTECTS BETTER THAN STONE COATING

Simply put, powder coating provides superior protection on metal roofing panels due to its method of application and ability to permanently bond with the metal surfacing. Stone coating relies on an adhesive to hold the ceramic chips in place, which is problematic for several reasons. Inconsistencies in the adhesive application, poor preparation of the panel during coating, and varying levels of thickness of the chips can all result in panel delamination and chip loss, as shown in the photos below.

Failed stone coating on metal roofing
Edge delamination of stone coating on metal roof
Failed stone coated metal roofing
Failed stone coated metal roofing surface
Failed stone coated metal roofing
Color fading evident on a stone coated roof

DIFFERENCES IN IMPACT RESISTANCE

While both stone and powder coating provide superior protection against impact resistance when compared with asphalt shingles, the effect of large hail on stone coated panels is similar. While it takes larger hail to damage stone coating, strong impacts can cause the stone chips to crack or dislodge, potentially compromising the integrity of the roof. However, since powder coating is molecularly adhered to the metal, impacts will not delaminate the material, unless the metal panel itself is punctured. 

The photo to the right shows a powder coated metal panel that was impacted by a large tree fall after a local tornado. While significant damage to the metal panel occurred, due to the sheer weight of the tree, the powder coating granules were not dislodged or affected. This enhanced durability and longevity of powder coating versus stone coating is a significant advantage to the long-term performance of the metal roofing system. 

For either finish, if the granules are dislodged, the underlying metal is now exposed to the elements and the underlying steel will begin to corrode. Since stone coated roofing is more susceptible to granule loss due to impacts, this is a concern for these types of systems. 

DIFFERENCES IN COLOR INTEGRITY

Faith Assembly Church metal roof
Metal Tile Series roof installed in 2008 in Orlando, Florida

As you can see in the photo above, if the granules on a metal panel come off, the color of the panel significantly changes color. Not only is this detrimental to the structural integrity of the panel, the aesthetics of the roof is compromised as well. Powder coated roofing retains its granules, due to its composition, ensuring the roof remains the same vibrant color for decades to come.

Another cause of color fading for stone coated roofing lies in the ceramic chips themselves, that are adhered to the metal panel. Over time, exposure to UV radiation from the sun can cause the pigments on the chips to fade, changing the color of the panel. While this isn’t a structural problem, it certainly affects the look of the roof. 

CONCLUSION

Why both powder and stone coating finishes are common on premium metal roofing panels, powder coating offers superior protection for steel and aluminum roofing products. Since powder coating doesn’t rely on an adhesive for granule retention, it offers better long-term metal coverage, won’t fade in color, or lose granules due to hail and animal impacts. Once baked and cured, powder coating offers more uniform and even coverage, becomes permanently bonded to the metal, and will provide decades of protection for the underlying metal.  With our premium base metal paint and exclusive powder coating, MMR’s metal roofing panels are built to last for decades to come!

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